Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chapter 5 Chemical Quantities and Reactions 5.3 Chemical Reactions and Equations 1

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Chemical Changes A chemical change occurs when a substance is converted into one or more substances with different formulas and different properties may be observed by the formation of bubbles, a change in color, or production of a solid 2

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Visible Evidence of a Chemical Reaction 3

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Which of the following represent a chemical change? A. burning a candle B. ice melting C. toast burns D. water turns to steam 4

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Which of the following represent a chemical change? A. burning a candlechemical change B. ice melting C. toast burnschemical change D. water turns to steam 5

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Writing a Chemical Equation 6

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Symbols Used in Chemical Equations To write a chemical equation an arrow indicates reactants form products reactants are written on the left side of the arrow products are written on the right side of the arrow multiple reactants or products are separated by a + sign the delta {Δ} sign indicates that heat is used to start the reaction 7

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Symbols Used in Chemical Equations 8

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Identifying a Balanced Equation In a balanced chemical equation, no atoms are lost or gained the number of reacting atoms is equal to the number of product atoms 9

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Balancing a Chemical Equation 10

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Balancing a Chemical Equation: Formation of Al 2 S 3 Step 1 Write an equation using the correct formulas of the reactants and products. Al(s) + S(s) Al 2 S 3 (s) Step 2 Count the atoms of each element in the reactants and products. 11 ReactantsProducts 1 atom Al2 atoms Al Not balanced 1 atoms S3 atoms S Not balanced

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Balancing a Chemical Equation: Formation of Al 2 S 3 Step 3 Use coefficients to balance each element. Starting with the most complex formula, change coefficients to balance equation. 2Al(s) + 3S(s) Al 2 S 3 (s) Step 4 Check the final equation to confirm it is balanced. Make sure coefficients are the lowest ratio. 12 ReactantsProducts 2 atoms Al2 atoms Al Balanced 3 atoms S3 atoms S Balanced

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) 13

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. A. P 4 (s) + 6Br 2 (l) 4PBr 3 (g) 14 ReactantsProducts P atoms44 Br atoms12

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations. B. 2Al(s) + Fe 2 O 3 (s) 2Fe(s) + Al 2 O 3 (s) 15 ReactantsProducts Al atoms22 Fe atoms22 O atoms33

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Balance the following equation, Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) 16 ReactantsProducts Atoms Fe Atoms O Atoms H

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Balance the following equation, Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) Step 1 Write an equation using the correct formulas of the reactants and products. Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) 17

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Step 2 Count the atoms of each element in the reactants and products. Fe 3 O 4 (s) + H 2 (g) Fe(s) + H 2 O(l) 18 ReactantsProducts Atoms Fe31 Atoms O41 Atoms H22

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution Step 3 Use Coefficients to balance each element. Fe 3 O 4 (s) + 6H 2 (g) 2Fe(s) + 3H 2 O(l) Step 4 Check the final equation to confirm it is balanced. 19 ReactantsProducts Atoms Fe 31 Atoms O41 Atoms H22

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Balancing Equations with Polyatomic Ions 20

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Balancing Equations with Polyatomic Ions When balancing equations with polyatomic ions, balance each polyatomic ion as a unit. 2Na 3 PO 4 (aq) + 3MgCl 2 (aq) Mg 3 (PO 4 ) 2 (s) + 6NaCl(aq) 21 ReactantsProducts PO 4 3 − ions22 Na + ions66 Mg 2+ ions33 Cl − ions66

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Learning Check Balance and list the coefficients from reactants to products. A. __Fe 2 O 3 (s) + __C(s) __Fe(s) + __CO 2 (g) 1) 2, 3, 2, 3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 B. __Al(s) + __FeO(s) __Fe(s) + __Al 2 O 3 (s) 1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 C. __Al(s) + __H 2 SO 4 (aq) __Al 2 (SO 4 ) 3 (aq) + __H 2 (g) 1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3 22

Chemistry An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition Copyright © 2012 by Pearson Education, Inc. Solution A. 2) 2, 3, 4, 3 2Fe 2 O 3 (s) + 3C(s) 4Fe(s) + 3CO 2 (g) B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al 2 O 3 (s) C. 2) 2, 3, 1, 3 2Al(s) + 3H 2 SO 4 (aq) 1Al 2 (SO 4 ) 3 (aq) + 3H 2 (g) 23